The proposed K01 Award provides the candidate with the skills needed to achieve her long-term goal of becoming an independent investigator in the field of biomedical HIV prevention focused on transgender women (TW). To do this, the candidate will submit an R01 to develop TW-focused strategies to improve adherence to long-acting HIV prevention products (e.g., cabotegravir injections). However, she must accomplish following training goals: 1) obtain training in the formative work of adherence intervention development within the context of biomedical HIV prevention trials to support the use of long-acting products, 2) gain skills to develop and pilot test an mHealth smartphone app to support adherence to long-acting biomedical HIV prevention strategies, 3) gain experience developing, running, and evaluating trials of behavioral interventions to support the use of biomedical products, and 4) build experience working with TW within the context of HIV prevention research. Training will expand the candidate's ability to integrate behavioral science and biomedical HIV prevention, develop/test adherence interventions that incorporate the appropriate context of participants' lives, and work with a high-risk vulnerable group (TW) to fit HIV prevention tools/interventions to their needs to increase their long-term effectiveness; three key NIH priorities. To do this, the candidate will engage in coursework, directed readings, one-on-one meetings with mentors, hands-on research activities, and completion of an independent research project. TW have unique challenges related to HIV prevention medication adherence. Left unaddressed, these challenges will prevent TW from accessing the promising long-acting HIV prevention tools in the development pipeline. The candidate will develop a replicable process to tailor the delivery of these tools and an adherence intervention (that will include an mHealth app) to the needs of TW, using the example of inert injectable cabotegravir. Work builds on a pilot study (PI: Rael) to identify tailored methods to deliver injectable cabotegravir in TW. The candidate will use qualitative methods (e.g., interviews, group discussions called ?Design Sessions?) to design the adherence intervention and the mHealth app. Then, she will execute a partially randomized patient-preference trial to determine if TW are able to use tailored injection strategies (injection at home or in walk-in clinics) to improve adherence, compared to a control group of TW who will engage a protocol based on HPTN-083/084. This will serve as a ?proof of concept? for the future R01 that will test this on a larger scale. Research and training will take place at NYSPI/Columbia, in affiliation with, 1) Project AFFIRM, a study of transgender identity (R01HD079603; PI: Bockting), that will provide infrastructure for critical research activities (e.g., recruitment), and 2) SLAP-HIV, a clinical trial to produce a long-acting form of cabotegravir (e.g., injection; UM1 AI120184; PI: Hope). SLAP-HIV will provide clinical oversight (e.g., ensure tailored delivery strategies are feasible) and the opportunity to interface with a clinical trial. Research findings and skills obtained during the K01 are applicable to other long-acting HIV prevention tools and risk groups.